1. Field of the Invention
The present invention relates to an optical element comprising a liquid crystalline polymer whose molecules are oriented, and, more particularly, to a method of producing an anisotropic optical element having anisotropic optical properties with respect to a direction of a normal to an element plane.
2. Background Art
Optical elements comprising liquid crystalline polymers of such liquid crystals as cholesteric, nematic, or discotic liquid crystals have been generally known as optical elements of the above-described type. These optical elements function as reflecting elements, optical compensation elements, optical retardation elements, etc., and are used as optical components of liquid crystal panel displays, security appliances, optical-measuring devices, optics, liquid crystal projectors, rear projection televisions, projection screens, and so on.
Of these optical elements, optical elements comprising cholesteric liquid crystals typically function as reflecting elements that reflect a specific component of a polarized light owing to the liquid crystalline structures (helical structures) of the cholesteric liquid crystals. For example, in liquid crystal panel displays, such reflecting elements are used as optical components such as polarized-light-separating reflecting elements, color filters, and negative C plate optical compensation elements. Further, in projection screens on which an image light is projected from a projector, such reflecting elements are used as polarization screens that reflect only a specific polarized component of the image light (see Japanese Patent Laid-Open Publication No. 2005-003823).
In an optical element comprising a cholesteric liquid crystal as described above, directions of helical axes or a mean direction of the directions of helical axes (a main direction of helical axes) in the liquid crystalline structure (helical structure) of the cholesteric liquid crystal has been perpendicular to an element plane, and optical properties of the optical element have therefore been isotropic with respect to a direction of a normal to the element plane.
In the above-described liquid crystal panel displays and projection screens, anisotropic optical properties have been demanded in an increasing number of cases in recent years. Specifically, a possible example of such cases is that, in a projection screen, an angle at which an image light emerges as a reflected light from the projection screen and another angle at which the image light emerges as an interfacial-reflected light from the projection screen are made different from each other so that mirroring of a light source is not recognized by viewers.
However, in the above-described optical elements comprising cholesteric liquid crystals, there has so far existed no practical method for producing an optical element having optical properties that are anisotropic with respect to a direction of a normal to an element plane.